The present invention is directed to a cylindrically shaped, radially expandable intravascular endoprosthesis formed of biocompatible material. The device is intended to be transported and introduced into the area of stenosis or obstruction of a blood vessel by means of a catheter with a guidewire in a relatively tightly wound or rolled-up state. Means are provided to temporarily hold the endoprosthetic device or stent in a wound or rolled-up state around the catheter during transport and introduction into said area.
There are different kinds of intravascular endoprostheses, commonly called stents, which have the common characteristic of being presented into a patient's blood vessel or other body cavity or lumen in the shape of a cylindrical cuff, the wall of which forms a kind of lattice of deformable mesh in order to permit its diametrical expansion and contraction. In one of these types such as shown in U.S. Pat. No. 4,740,207 (Kreamer), the stent is made of stainless steel sheet and appears originally in a rolled-up form of smaller diameter. After being introduced into the area of the vessel to be treated, it is expanded by means of an angioplasty balloon on the distal end of a catheter which is disposed on the interior of the rolled-up stent. The balloon is inflated with a fluid to the desired diameter which usually corresponds to the maximum expansion of which said balloon is capable.
In another type, such as described in U.S. Pat. No. 3,868,956, and Japanese Application 57-89859 published Jun. 4, 1982, the stent is made of thermo-expandable material such as nitinol which is dilated by heat after being implanted.
Finally, in a recently developed type, the stent is made of stainless steel wires of good elastic quality which are interwoven into a mesh, the diameter of which is selected to be slightly larger than the normal inner diameter of the vessel to be treated, so that it can exert a residual radial pressure on the arterial wall after being implanted. Before being introduced into the patient's blood vessel and while advancing the stent into the area of the blood vessel to be treated, the stent is reduced in diameter by stretching longitudinally and kept compressed on the catheter by a withdrawable sleeve. Once the device is implanted, the progressive withdrawal of said membrane permits the deployment of the stent in the vascular lumen.
Of these three known kinds of stents, the second, the one made of thermo-expandable material, presents great inconvenience because it is difficult to manipulate and implant, and its expansion is hard to control and is not reliable.
The above inconvenience does not exist in the stents made of stainless steel wire, but they still present a defect in that their expansion to a desired maximum diameter takes place at the cost of a proportional shortening of their length. This shortening, which follows the geometrical deformation of the lattice mesh being expanded in the transverse direction of the cylinder and reduced in the direction of its length, has the effect of making the accurate implantation of the device at its desired location very difficult.
The structure of an open weave, stainless steel wire results in loose wires at the ends of the cylinder which can be traumatizing to the arterial tissue and can result in a fibrous change therein and the formation of an intraluminal scar which can be the beginning of another stenosis.
The invention has the purpose of eliminating these inconveniences, particularly to provide a stent which can be easily and accurately placed in the desired arterial location with considerably less trauma than the prior art devices.